This invention relates to pipe bending machines, and more particularly to a pressure die having a symmetrical and reversible exit block.
Pipe bending machines include die halves or die blocks having cavities or grooves for receiving and contacting the pipe or tubing during the bending operation (hereinafter collectively referred to as “pipe”). Typically, a pipe bending machine comprises at least two dies, a pressure die and a forming die. The pressure die applies bending pressure to the pipe around the curvature of the forming die. The forming die, pressure die, or both rotate relative to the other to achieve the required bending pressure to bend the pipe.
One problem with traditional pipe bending devices and techniques is that the round shape of the pipe deforms or flattens as the pipe is bent around the forming die. The reason for this deformation is that as the pipe is bent, the outer portion of the pipe is drawn in the direction of the bend, which flattens the outer portion of the pipe. Devices such as the ones disclosed in U.S. Pat. Nos. 5,694,800, 5,469,728, and 5,345,802 have tried to overcome the pipe deformation problem by narrowing the curvilinear geometry of the groove at the exit end of the pressure die so that the exit end of the groove is narrower than the pipe before it is bent. These patents disclose that narrowing the exit end of the pressure die groove causes high axial frictional forces allowing the pressure die to draw the pipe during bending since the narrowed end has a smaller radius than the pipe before it is bent. These patents disclose a space beneath the pipe and the groove of the pressure die so that as the pipe is being drawn, it is also being forced toward the surface of the groove, which causes the pipe to conform to the exit edge of the exit block groove (it ovals the pipe).
Another problem with many pressure dies is that they become worn out quickly due to the considerable forces placed on them by pipes during bending operations. The user must replace the pressure die when it becomes worn so that the narrowed end of the pressure die remains able to grab and draw the pipe during bending. The replacement of pressure dies can be expensive because at least a portion of the pressure die must be made of an expensive high density metal strong enough to withstand considerable force.
Therefore, there is a need for a pressure die which efficiently bends pipe with minimal pipe deformation, and has an improved life thereby reducing the frequency at which new pressure dies must be purchased by the user.